The present invention relates to a quantum well structure composed of a quantum well layer and a carrier confinement layer of an energy gap greater than that of the former, and a semiconductor device employing such a quantum well structure.
A physical phenomenon, such as light emission or absorption by substances (materials), or a tunneling transport of electrons in electron devices, has recently come into wide use in semiconductor devices employing the quantum well structure in the field of electronics and is now a driving force in opening up new key industries. However, such a physical phenomenon largely depends on the energy gap intrinsic to the material used and hence is limited in its application accordingly.
Now, a conventional light emitting semiconductor device will be described as a concrete example.
Because of their excellent features such as small size, light weight, and high efficiency, light emitting semiconductor devices are now being used widely in fiber optic communications and various instrumentations as well as in magneto-optical disks, compact disks, laser printers, miniature display lamps, and various other terminal equipments. For further broading of their application it is of enormous importance to enlarge the range of emission wavelength of the light emitting semiconductor devices. There is a demand for green to blue light sources in the visible region and, in the infrared region, for light sources for analysing special gases and for fluoride fiber optic communications.
Conventional light emitting devices utilize, for emitting light, photons of an energy corresponding to the energy gap of the light emitting layer as mentioned above, and consequently, in case of changing the wavelength of light, they are subject to severe limitations in terms of materials used. This presents a serious problem in that the implementation of a blue light emitting device and an intermediate infrared light emitting device, in particular, is difficult.
Such a difficulty is experienced not only in light emitting devices but also in photo detectors. In the field of electronic devices many attempts are also being made for sophistication of the electron transport phenomenon by mutually combining various materials of different energy gaps, but these attempts are also limited basically by the energy gaps inherent to the materials used.